I'm new to the travel trailer game. So I do have a lot of qustions, but minimal time right now, so I'll ask my most immediate question & it has to deal with the hot water tank. I know how to turn it on outside & flip the switch on the inside but is there a tank it will heat up or is it more of an on demand hot water unit? I have a 2008 rockwood roo 21ss - no manuals

Congrats on the new camper and welcome to the forum. As NWJeeper said, there is a tank that holds either 6 or 10 gallons. That gets heated and is where the hot water comes from.
Any other questions, be sure to ask.

I'm new to the travel trailer game. So I do have a lot of qustions, but minimal time right now, so I'll ask my most immediate question & it has to deal with the hot water tank. I know how to turn it on outside & flip the switch on the inside but is there a tank it will heat up or is it more of an on demand hot water unit? I have a 2008 rockwood roo 21ss - no manuals

To answer your question, your 6 or 10 gal tank heats up the water inside the tank to a certain degree so when ever you want hot water, its there. It doesn't just come on when you need hot water. Just make sure there is water in the tank when you turn on the electric element. Without water, the element will burn out.

To fill it up just connect your city water supply up and turn on a hot water faucet in the rig till water starts flowing well. Your HW tank is now full. As far as where the tank is located... look for a white metal panel on the outside of your rig about 18"x18" or so. It'll have a mesh screen about 6"x5" or so for air intake. The panel will fasten at the top with a small plastic "ring" on a spring and be hinged at the bottom. You also may have a 110V power toggle switch on the HWH itself.

first, you aren't missing much not having the manuals. most are from individual manufacturers and deal with the specific appliances or products.
the FR owner's manual is a joke. very generic and helps very little.
you can download the manuals to almost all the appliances, including the water heater, from each of the manufacturers' websites. it's a Suburban so find the model # and go to the website.

the water heater should be in a cabinet, just inside the city water hookup.
also, the FW tank will be the other source of water, by way of the water pump.
your DSI switch will use propane to light the burner to heat the water. the electric switch on the WH is for using the electric element to heat the water.
electric takes longer but is cheaper if you have hookups.